Frictional Fluid Dynamics I

What happens when you inject gas into a wet granular material? Amazing patterns emerge! This is a time lapse movie showing the incremental growth of fingers of air into a wet granular fluid mixture which is contained in a narrow gap between to glass plates (a Hele-Shaw cell). The dynamics changes abruptly when we increase the amount of granular material in the mixture: the system becomes highly intermittent, and “stick slip” bubbles appear. The experiments took a day to complete, and the channel is 20 cm wide.